The present disclosure relates to systems and methods for percutaneous implantation of a heart valve prosthesis. More particular, it relates to delivery systems and methods of stepped deployment of prosthetic heart valves.
A human heart includes four heart valves that determine the pathway of blood flow through the heart: the mitral valve, the tricuspid valve, the aortic valve, and the pulmonary valve. The mitral and tricuspid valves are atrioventricular valves, which are between the atria and the ventricles, while the aortic and pulmonary valves are semilunar valves, which are in the arteries leaving the heart. Ideally, native leaflets of a heart valve move apart from each other when the valve is in an open position, and meet or “coapt” when the valve is in a closed position.
Problems that may develop with valves include stenosis in which a valve does not open properly, and/or insufficiency or regurgitation in which a valve does not close properly. Stenosis and insufficiency may occur concomitantly in the same valve. The effects of valvular dysfunction vary, with regurgitation or backflow typically having relatively severe physiological consequences to the patient.
Diseased or otherwise deficient heart valves can be repaired or replaced with an implanted prosthetic heart valve. Conventionally, heart valve replacement surgery is an open heart procedure conducted under general anesthesia, during which the heart is stopped and blood flow is controlled by a heart-lung bypass machine.
Traditional open surgery inflicts significant patient trauma and discomfort, and exposes the patient to a number of potential risks, such as infection, stroke, renal failure, and adverse effects associated with the use of the heart-lung bypass machine, for example.
Due to the drawbacks of open-heart surgical procedures, there has been an increased interest in minimally invasive replacement of cardiac valves. Recently, prosthetic valves supported by stent frame structures that can be delivered percutaneously using a catheter-based delivery system have been developed for heart and venous valve replacement.
With these percutaneous transcatheter (or transluminal) techniques, a valve prosthesis is compacted for delivery via a catheter and then advanced, for example, through an opening in the femoral artery and through the descending aorta to the heart, where the prosthesis is then deployed in the annulus of the valve to be repaired (e.g., the aortic valve annulus).
Percutaneously delivered prosthetic valves may include either self-expandable, balloon-expandable, and/or mechanically-expandable stent frame structures with a valve structure attached or coupled to the interior of the stent frame structure. The prosthetic valve may be reduced in diameter, by crimping onto a balloon catheter or by being contained within a sheath component of a delivery catheter, and advanced through the venous or arterial vasculature.
Once the prosthetic valve is positioned at the treatment site, for instance within an incompetent native valve, the stent frame structure may be expanded to hold the prosthetic valve firmly in place. One example of a stented prosthetic valve is disclosed in U.S. Pat. No. 5,957,949 to Leonhardt et al., which is incorporated by reference herein in its entirety.
Although transcatheter techniques have attained widespread acceptance with respect to the delivery of conventional stents to restore vessel patency, only mixed results have been realized with percutaneous delivery of a relatively more complex prosthetic heart valve.
Various types and configurations of prosthetic heart valves are available, and continue to be refined. The actual shape and configuration of any particular prosthetic heart valve is dependent to some extent upon native shape and size of the valve being repaired (i.e., mitral valve, tricuspid valve, aortic valve, or pulmonary valve). In general, prosthetic heart valve designs attempt to replicate the functions of the valve being replaced and thus may include a valve structure comprising one or more leaflet-like structures.
With a bioprosthesis construction, the replacement valve may include a valved vein segment that is mounted in some manner within an expandable stent frame to make a valved stent (or “stented prosthetic heart valve”). For many percutaneous delivery and implantation systems, the self-expanding valved stent is crimped down to a desired size and held in that compressed state within an outer sheath, for example. Retracting the sheath from the valved stent allows the stent to self-expand to a larger diameter, such as when the valved stent is in a desired position within a patient.
In other percutaneous implantation systems, the valved stent can be initially provided in an expanded or uncrimped condition, then crimped or compressed on a balloon portion of a catheter until it is as close to the diameter of the catheter as possible. Once delivered to the implantation site, the balloon is inflated to deploy the so-configured prosthesis. With either of these types of percutaneous stent delivery systems, conventional sewing of the prosthetic heart valve to the patient's native tissue is typically not necessary.
It is imperative that the stented prosthetic heart valve be accurately positioned relative to the native valve immediately prior to deployment from the catheter as successful implantation requires the transcatheter prosthetic heart valve intimately lodge and seal against the native tissue. If the prosthesis is incorrectly positioned relative to the native tissue, serious complications can result as the deployed device can leak and may even dislodge from the implantation site.
In an effort to enhance the accuracy of the prosthetic heart valve placement, imaging technology has been utilized to assist a clinician in better evaluating the position of the transcatheter prosthetic heart valve immediately prior to deployment and implantation.
In light of the above, although there have been advances in percutaneous valve replacement techniques and devices, there is a continued desire to provide different delivery systems for delivering cardiac replacement valves, and in particular, expandable stented prosthetic heart valves, to an implantation site in a minimally invasive and percutaneous manner.